Rotate a clip
1Select the clip in the Timeline.
2In the Effects view, click the Edit Effects button.
3Expand the Motion effect in the Properties view, and do one of the following:
•Drag the underlined value to the right of Rotation.
•Click Rotate Left or Rotate Right to rotate the clip 90° in either direction.
If you mean rotating the entire frame (not just the video) to portrait view the answer is: not possible.
Next time film with the smartphone in landscape position.
Another way that also works....
Select the clip > Right click > Select "Rotate 90 Left" or "Rotate 90 Right"
the rotate selection is not available or it would be easy. why it's not shaded , so you can rotate 90 degrees I don't know.
Please post a screenshot.
Make sure that you don't have multiple clips selected.